<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>双向判断语句</title>
</head>
<body>
<script type="text/javascript">
var num1 = 300;
var num2 = 150;
if (num1 < num2) {
    alert('你好，条件成立');
} else {
    alert('对不起，条件不成立');
}
alert('演示完成');
</script>
</body>
</html>